This application claims priority-under 35 USC 119 from Japanese patent applications, No. 2002-210113, No. 2002-210114 and No. 2002-210115, the disclosure of which is incorporated by reference herein.
1. Field of the Invention
The present invention relates to an exposure device. Particularly, the invention relates to an exposure device including a plurality of kinds of light-emitting elements with different light-emitting spectra, which are placed at intersections of matrix electrodes, for performing superior in gradation reproducibility.
2. Description of the Related Art
An organic EL (Electro-Luminescent) element, which employs a fluorescent organic substance for a light-emitting layer thereof, can be easily manufactured compared with other types of light-emitting elements. The organic EL element enables to manufacture a thin, light-weight light-emitting element. Owing to such features, the organic EL elements have been researched and developed to use them as elements for thin display. In recent years, high-performance organic EL elements comparable to light-emitting diodes (LEDs) have been developed in terms of light-emitting luminance, efficiency and durability. Consequently, the application of such organic EL elements has been studied to an exposure device for exposing photosensitive materials such as silver halide photosensitive material.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2000-103114 has disclosed an exposure device using organic EL elements. As shown in FIG. 8, element rows, each formed by arranging a plurality of organic EL elements 80 for emitting lights with respective colors of red (R), green (G) and blue (B) in a main scanning direction for the respective colors, are grouped into sets of three RGB colors. Such sets (2 sets in FIG. 8) are arranged in the sub-scanning direction. In FIG. 8, each alphabet (R/G/B) that represents its corresponding color is put to the ends of respective symbol in order to discriminate between the organic EL elements 80 of the respective RGB colors.
In this exposure device, each of the light rays of RGB colors is applied to the same position of a photosensitive material once every sub-scanning process so that a full color latent image is formed on the photosensitive material. Moreover, an unillustrated control circuit controls the light-emission intensity and light-emission time of each organic EL element. A predetermined exposure gradation is achieved for each of the RGB colors. For example, assuming that exposure gradations of m-steps are available for each color, the number of possible color developments of this exposure device is represented by m3. Thus, in order to obtain multiple color developments, the number m of exposure gradations is required to increase. For example, in order to increase the number of exposure gradations in exposure control in the pulse-width modulation system and pulse number modulation system, the minimum pulse time width needs to be smaller.
It is difficult to control the driving current of the light-emitting element such as organic EL elements with high precision by using a fine pulse time width, from the viewpoint of control precision of the control circuit. Moreover, when the organic EL element is used as a light-emitting element, even if the pulse time width of the driving current is controlled with high precision, the response speed of the organic EL element does not properly follow the pulse. Thus, it is difficult to increase the number of exposure gradations. Furthermore, even with the exposure control in the intensity modulation system, it is difficult to control the driving current in fine steps with high precision. In other words, conventionally, when the respective light-emitting elements constituting the exposure device are gradation-modulated in multiple stages so as to carry out exposing processes, the number of exposure gradations is limited.
The control circuit controls the light-emitting intensity and light-emitting time of each organic EL element. A predetermined exposure gradation is achieved for each of the RGB colors. For example, assuming that exposure gradations of m-steps are available for each color, the number of possible color developments of this exposure device is represented by m3. Thus, in order to obtain multiple color developments, the number m of exposure gradations needs to increase. For example, in order to increase the number of exposure gradations in exposure control in the pulse-width modulation system and pulse number modulation system, the minimum pulse time width needs to be smaller.
Each photosensitive material has a different sensitivity to each of light rays of the respective colors. Thus, with respect to a color having a low sensitivity, an exposing process is required to be with a higher light-emitting intensity. In this case, the service life of the light-emitting element having a color that requires a high light-emitting intensity tends to become particularly shorter compared with the light-emitting element with the other colors. Thus, the service life of the exposure device is limited by the light-emitting element having the shortest service life. When the photosensitive material is a silver halide photosensitive material, the sensitivity to red light is lower than the sensitivity to green light or blue light in the order of not less than one digit. Thus, the light-emitting intensity of the red color light-emitting element needs to increase. Consequently, the shorter the service life of the light-emitting element of red color becomes, the shorter the shorter service life of the exposure head will become.
Generally, the greater the number of element rows becomes, the more the light-emitting intensity can reduce on a time average basis and the more reliable the exposure device will become. In contrast, the exposure device will become larger, resulting in degradation in the production yield and an increase in costs. This means that the total number of the element rows has an appropriate upper limit. Thus, the reliability of the entire exposure device is demanded to improve while maintaining the total number of the element rows in a fixed value.
For example, assuming that exposure gradations of m-steps are available for each color, the number of possible color developments of this exposure device is represented by m3. In order to obtain multiple color developments, the number m of exposure gradations needs to increase. For example, in order to increase the number of exposure gradations in exposure control in the pulse-width modulation system and pulse number modulation system, the minimum pulse time width needs to be smaller.
Each photosensitive material has a different sensitivity to each of light rays of the respective colors. Thus, with respect to a color having a low sensitivity, an exposing process needs to be with a higher light-emitting intensity. Here, the service life of the light-emitting element having a color that requires a high light-emitting intensity tends to become particularly shorter compared with the light-emitting element with the other colors. Thus, the service life of the exposure device is limited by the light-emitting element having the shortest service life. When the photosensitive material is a silver halide photosensitive material, the sensitivity to red light is lower than the sensitivity to green or blue light in the order of not less than one digit. Thus, the light-emitting intensity of the red color light-emitting element needs to increase. Consequently, the service life of the light-emitting element of red color becomes shorter and the service life of the exposure head becomes shorter.
The present invention has been devised to meet the above-mentioned demands. An object of the invention is to provide an exposure device capable of increasing significantly the number of exposure gradations exceeding the conventional limit.
Another object of the invention is to reduce the light-emitting intensity of the light-emitting element that has the lowest sensitivity in the photosensitive material on a time average basis and consequently to provide an exposure device with superior reliability.
Still another object is to provide an exposure device with superior reliability.
According to a first aspect of the present invention, an exposure device has a light-emitting element array and a control device. The light-emitting element array has a plurality of element rows, each of which has a plurality of light-emitting elements with substantially the same light-emitting spectrum. At the elements, the exposure gradation can be controlled independently at m (mxe2x89xa73) stages. The light-emitting elements are aligned in a main scanning direction that intersects the sub-scanning direction. Such rows are aligned in the sub-scanning direction and at least n (nxe2x89xa72) number of light-emitting elements are aligned in the sub-scanning direction. The control device assigns exposure gradations to each of the n number of light-emitting elements aligned in the sub-scanning direction according to the respective gradations obtained when a range from shadow to highlight is represented by {nxc3x97(mxe2x88x921)+1} stages. Based upon the exposure gradations thus assigned, the control device controls each of the above-mentioned n-number of light-emitting elements so that the same position of the photosensitive material is subjected to multiple exposing processes of n times at maximum.
Regarding the light-emitting elements, independent control of the exposure gradation at m (mxe2x89xa73) stages is available. This exposure device employs the light-emitting element array as follows. The light-emitting element array has a plurality of element rows. Each of the element rows has a plurality of light-emitting elements, each of which has substantially the same light-emitting spectrum. The elements are aligned in the main scanning direction that intersects the sub-scanning direction. Such element rows are aligned in the sub-scanning direction in order to align at least n (nxe2x89xa72) number of light-emitting elements in the sub-scanning direction. In this exposure device, exposure gradations can be assigned according to the respective gradations obtained when each of the n number of light-emitting elements aligned in the above-mentioned sub-scanning direction is represented by {nxc3x97(mxe2x88x921)+1} stages with respect to shadow to highlight. Then, based upon the assigned exposure gradations, the control device controls each of the above-mentioned light-emitting elements so that the same position of the photosensitive material is subjected to multiple exposing processes of n times at maximum. In this way, the exposing dose control of {nxc3x97(mxe2x88x921)+1} gradations can be performed. With this arrangement, the exposure gradations can increase significantly exceeding the conventional limit.
In order to achieve one of the above-mentioned objectives, another exposure device of the invention has a light-emitting element array having p (pxe2x89xa72) kinds of light-emitting elements with different light-emission spectra. This exposure device also has a control device. The array has a plurality of element rows, each of which has a plurality of light-emitting elements. In the light-emitting elements, the exposure gradation can be controlled in mi (mixe2x89xa73, i is an integer of 1 to p) stages independently for each of the kinds. The light-emitting elements are aligned in the main scanning direction that intersects the sub-scanning direction. Such rows are aligned in the sub-scanning direction and at least ni (nixe2x89xa72, i is an integer of 1 to p) number of light-emitting elements are aligned in the sub-scanning direction for each of the kinds. The control device assigns exposure gradations to each of the ni number of light-emitting elements aligned in the sub-scanning direction according to the respective gradations obtained when a range from shadow to highlight is represented by {nixc3x97(mixe2x88x921)+1} stages. Based upon the exposure gradations thus assigned, the control device controls each of the above-mentioned ni-number of light-emitting elements so that the same position of the photosensitive material is subjected to multiple exposing processes of ni times at maximum.
In this arrangement, the light-emitting array has p (pxe2x89xa72) kinds of light-emitting elements having different light-emission spectra and a structure in which a plurality of element rows. Each of the element rows has a plurality of light-emitting elements which the exposure gradation can be controlled in mi (mixe2x89xa73, i is an integer of 1 to p) stages independently for each of the kinds. The light-emitting elements are aligned in the main scanning direction that intersects the sub-scanning direction. Such element rows are also aligned in the sub-scanning direction so that at least ni (nixe2x89xa72, i is an integer of 1 to p) number of light-emitting elements are aligned in the sub-scanning direction for each of the kinds. Exposure gradations can be assigned according to the respective gradations obtained when each of the ni number of light-emitting elements aligned in the above-mentioned sub-scanning direction is represented by {nixc3x97(mixe2x88x921)+1} stages with respect to shadow to highlight.
Based upon the exposure gradations thus assigned, the control device controls the above-mentioned light-emitting elements and the same sub-scanning position of the photosensitive material is subjected to multiple exposing processes of ni times at maximum. Thus, the exposing dose control of {nixc3x97(mixe2x88x921)+1} gradations can be performed. As a whole, the exposing dose control of {nixc3x97(m1xe2x88x921)+1}xc2x7{n2xc3x97(m2xe2x88x921)+1}xc2x7xc2x7{npxc3x97(mpxe2x88x921)+1} gradations can be achieved. The number of exposure gradations increases significantly to exceed the conventional limit.
In an exposure device with the above-mentioned p kinds of light-emitting elements, the number of the first set of light-emitting elements may be greater than the number of other sets of the light-emitting elements. The first set of the elements emits light of the light-emitting spectrum having the lowest sensitivity to the photosensitive material among the p kinds of light-emitting elements that are aligned in the sub-scanning direction. The light-emitting intensity (time average) of the light-emitting elements having the lowest sensitivity to the photosensitive material will reduce and the reliability of the exposure device will thereby improve.
The light-emitting elements of p kinds may be prepared as three kinds of light-emitting element shaving light-emitting spectra that are capable of forming a full color image in association with the photosensitive materials. For example, the three kinds of light-emitting elements may be prepared as red light-emitting elements for emitting red light, green light-emitting elements for emitting green light and blue light-emitting elements for emitting blue light. With this arrangement, a full-color image (latent image) can be formed. Moreover, the number of exposure gradations for each kind may be arranged to satisfy the following equation.
{n1xc3x97(m1xe2x88x921)+1}={n2xc3x97(m2xe2x88x921)+1}= . . . ={npxc3x97(mpxe2x88x921)+1}
By setting the numbers of exposure gradations to the same value for the respective colors, accurate gray gradations can be achieved from black to white according to the respective exposure gradations.
There is a case that the light-emitting array is constituted by matrix electrodes in which a plurality of anodes and a plurality of cathodes are arranged in a lattice shape and light-emitting elements that are placed at the intersections of these matrix electrodes. The above-mentioned exposure device may be arranged as follows. Matrix electrodes of the light-emitting array are divided into a plurality of areas in the cathode array direction or the anode array direction. A drive device, which carries out a driving process independently to apply a voltage between the above-mentioned cathode and anode so that the light-emitting element placed at the intersection of the matrix electrodes of the corresponding area is lighted on, may be further provided for each of the divided areas.
There is a case that the entire light-emitting element group is driven by dividing the matrix electrodes into a plurality of areas, and applying a voltage between the cathode and anode for each of the areas in order to drive and activate the light-emitting element placed on each intersection of the matrix electrodes in the area independently. Compared with this case, the present invention can reduce the number of light-emitting elements to be assigned to each cathode or each anode, thereby improving the driving duty of each light-emitting element and reducing the peak light-emitting intensity. Consequently, the reliability of the exposure device improves. Here, the driving duty refers to a ratio t/T of the pulse width t with respect to the pulse repeating frequency T when the light-emitting elements are pulse-driven. Because the exposing efficiency improves by improving the driving duty, the peak light-emitting intensity of each light-emitting element will reduce.
When the exposure device is provided with a plurality of kinds of light-emitting elements having different light-emitting spectra, the area where light-emitting elements having the lowest sensitivity of the photosensitive material are aligned may be driven independent of other areas. With this independent driving, the peak light-emitting intensity of the light-emitting elements with the lowest sensitivity lowers, and the reliability of the exposure device will further improve.
In the above-mentioned exposure device, organic EL elements, which are easily formed into an array, are often used as light-emitting elements. A number of organic EL elements can be formed on a single substrate by using a coating method and an ink-jet method in addition to a vacuum vapor deposition. When the organic EL element is used as the light-emitting element in the exposure device, the productivity of the device will improve, and time-consuming tasks for adjusting the layout positions of the respective light-emitting elements will be eliminated. Thus, the layout positions are maintained with high precision. With respect to the substrate on which a light-emitting array is formed, a TFT (thin-film transistors) substrate is often used. Each light-emitting element will be able to perform an exposure gradation control at multiple stages by modulating at least one of the light-emitting intensity and exposing time so as to control the exposure gradations.
Here, the exposing dose control of {nxc3x97(mxe2x88x921)+1} gradations can be performed with an exposure device as follows. The exposure device has a light-emitting element array. The array has a plurality of element rows, each of which has a plurality of light-emitting elements. The elements with substantially the same light-emitting spectrum can be controlled independently in the exposure gradation in m (mxe2x89xa73) stages, and are aligned in the main scanning direction. The main scanning direction intersects the sub-scanning direction, and such elements are aligned in the sub-scanning direction in order to align at least n (nxe2x89xa72) number of light-emitting elements in the sub-scanning direction. Exposure gradations are assigned according to the respective gradations obtained when each of the n number of light-emitting elements aligned in the above-mentioned sub-scanning direction is represented by {nxc3x97(mxe2x88x921)+1} stages with respect to shadow to highlight. Based upon the exposure gradations thus assigned, the same position of the photosensitive material is subjected to multiple exposing processes of n times at maximum. With this exposing method, the exposure gradations can increase significantly exceeding the conventional limit.
Moreover, the exposing dose control of {nixc3x97(mixe2x88x921)+1} gradations can be performed with another exposure device. In other words, as a whole, the exposing dose control of {nixc3x97(m1xe2x88x921)+1}xc2x7{n2xc3x97(m2xe2x88x921)+1} . . . {npxc3x97(mpxe2x88x921)+1} gradations can be performed. The exposure device has a light-emitting element array. The array has a plurality of element rows. Each element row has p (pxe2x89xa72) kinds of light-emitting elements with different light-emission spectra. Each of the elements can be controlled independently in the exposure gradation in mi (mixe2x89xa73, i is an integer of 1 to p) stages for each of the kinds. The elements are aligned in the main scanning direction that intersects the sub-scanning direction. The element rows are aligned in the sub-scanning direction, and at least ni (nixe2x89xa72, i is an integer of 1 to p) number of light-emitting elements are aligned in the sub-scanning direction for each of the kinds. Exposure gradations are assigned according to the respective gradations obtained when each of the ni number of light-emitting elements aligned in the above-mentioned sub-scanning direction is represented by {nixc3x97(mixe2x88x921)+1} stages with respect to shadow to highlight. Based upon the exposure gradations thus assigned, each of the above-mentioned ni-number of light-emitting elements is controlled and a single position of the photosensitive material is subjected to multiple exposing processes of ni times at maximum. In this case, the number of exposure gradations will increase significantly exceeding the conventional limit.
Here, the exposure device of the invention is applicable to an exposure device of silver halide color photosensitive material. By using the silver halide color photosensitive material that is superior in gradation expressing property and gradation reproducibility, the exposure device of the present invention faithfully reproduces all the number of high exposure gradations.
According to a second aspect of the invention, there is provided an exposure device comprising a light-emitting element array. The array has a plurality of kinds of light-emitting elements that have different light-emitting spectra, with at least one light-emitting element with respect to each of the kinds being aligned in the sub-scanning direction. The plurality of kinds of light-emitting elements are arranged such that the number of a set of light-emitting elements is greater than the number of elements for each kind of the light-emitting elements in the sub-scanning direction. The set of light-emitting elements is to emit the light of the light-emitting spectrum having the lowest sensitivity with respect to the photosensitive material in the plurality of kinds of light-emitting elements. By using the plurality of light-emitting elements arranged in the sub-scanning direction, a single position of the photosensitive material is subjected to multiple exposing processes.
According to the exposure device of the second aspect, a light-emitting element array in which light-emitting elements of a plurality of kinds have different light-emitting spectra is provided. In this light-emitting element array, at least one light-emitting element is aligned with respect to each of the kinds in the sub-scanning direction so that by using the light-emitting elements arranged in the sub-scanning direction, the same position of the photosensitive material is subjected to multiple exposing processes. In this light-emitting element array, the plurality of kinds of light-emitting elements are arranged such that the number of a particular set of light-emitting elements is greater than the number of elements for each kind of the light-emitting element of the other kinds. The set of light-emitting elements has the lowest sensitivity (that is, emitting the light of the light-emitting spectrum with the lowest sensitivity) with respect to the photosensitive material of the above-mentioned plurality of kinds of light-emitting elements. Thus, the light-emitting intensity (time average) of the light-emitting element having the lowest sensitivity with respect to the photosensitive material reduces, and consequently the service life of the light-emitting elements prolongs. Consequently, the reliability of the exposure device improves.
The plurality of kinds of light-emitting elements may be prepared as light-emitting elements of three kinds that are provided with light-emitting spectra capable of forming a full-color image in association with the photosensitive material. For example, three kinds of light-emitting elements, that is, red light-emitting elements for emitting red light, green light-emitting elements for emitting green light and blue light-emitting elements for emitting blue light, may be prepared. Thus, a full-color image (latent image) can be formed. For example, when the above-mentioned photosensitive material is a silver halide photosensitive material, the number of elements of the red light-emitting elements is set to be greater than the number of blue light-emitting elements, and also greater than the number of green light-emitting elements.
For example, the light-emitting element array has p (pxe2x89xa72) kinds of light-emitting elements with different light-emission spectra. The array has a plurality of element rows, each of which has a plurality of light-emitting elements that the exposure gradation can be controlled at mi (mixe2x89xa73, i is an integer of 1 to p) stages in an independent manner respectively for each of the kinds. The elements are aligned in the main scanning direction that intersects the sub-scanning direction. Such rows are aligned in the sub-scanning direction and at least ni (nixe2x89xa72, i is an integer of 1 to p) number of light-emitting elements are aligned in the sub-scanning direction for each of the kinds. In this light-emitting element array, the number of element rows in which the light-emitting elements having the lowest sensitivity to the photosensitive material among the above-mentioned p-kinds of light-emitting elements may be greater than the number of other element rows. Each of other element rows is aligned according to each of the kinds of the light-emitting elements.
In this multi-gradation exposure device, exposure gradations can be assigned to the ni-number of respective light-emitting elements that are aligned in the sub-scanning direction according to the respective gradations obtained when gradations from shadow to highlight are represented by {nixc3x97(mixe2x88x921)+1} stages.
In the above-mentioned light-emitting element array, the number of rows of light-emitting elements that emit light having the lowest sensitivity to the photosensitive material in the above-mentioned p kinds of light-emitting elements is made greater than the number of rows of other kinds of light-emitting elements. Thus, the light-emitting intensity (time average) of the light-emitting elements having the lowest sensitivity to the photosensitive material can reduce. Thereby the service life of the light-emitting elements prolongs. Consequently, the reliability of the exposure device improves.
The above-mentioned multi-gradation exposure device often has a control device as well. Based upon the assigned exposure gradations, the control device controls each of the above-mentioned light-emitting elements so that the same position of the photosensitive material is subjected to multiple exposing processes of ni times at maximum. Thus, the exposing dose control of {nixc3x97(mixe2x88x921)+1} gradations can be performed. As a whole, the exposing dose control of {n1xc3x97(m1xe2x88x921)+1}xc2x7{n2xc3x97(m2xe2x88x921)+1} . . . {npxc3x97(mpxe2x88x921)+1} gradations can be performed. With this arrangement, the number of exposure gradations significantly exceeding the conventional limit can be achieved.
The number of exposure gradations for each kind is often arranged to satisfy the following equation. By setting the numbers of exposure gradations of the respective colors to the same value for the respective colors, the gradations from black to white can be expressed accurately according to the respective exposure gradations.
{n1xc3x97(m1xe2x88x921)+1}={n2xc3x97(m2xe2x88x921)+1}= . . . ={npxc3x97(mpxe2x88x921)+1}
There is a case when the light-emitting array is constituted by matrix electrodes in which a plurality of anodes and a plurality of cathodes are arranged in a lattice shape with light-emitting elements being placed at the intersections of these matrix electrodes. The above-mentioned exposure device is arranged such that matrix electrodes of the light-emitting array are divided into a plurality of areas in the cathode array direction or the anode array direction. A driving device may be further provided, which carries out a driving process independently to apply a voltage between the above-mentioned cathode and anode such that the light-emitting element placed at the intersection of the matrix electrodes of the corresponding area is activated.
In comparison with a case in which the entire light-emitting element group is driven, the number of light-emitting elements to be assigned to each cathode or each anode decreases in this exposure device. Accordingly, the driving duty of each light-emitting element improves and the peak light-emitting intensity decreases. This is due to dividing the matrix electrodes into a plurality of areas and applying a voltage between the above-mentioned cathode and anode for each of the areas in order to drive independent and activate the light-emitting element placed at each intersection of the matrix electrodes in the area. Consequently, the reliability of the exposure device improves.
When the exposure device has a plurality of kinds of light-emitting elements having different light-emitting spectra, the area in which light-emitting elements with the lowest sensitivity of the photosensitive material may be driven independently of the other areas among the plurality of kinds of the light-emitting elements. With this independent driving, the peak light-emitting intensity of the light-emitting elements with the lowest sensitivity lowers, the reliability of the exposure device improves.
In the above-mentioned exposure device, organic EL elements, which are easily formed into an array, are often used as light-emitting elements. A number of organic EL elements can be formed on a single substrate by using a coating method and an ink-jet method in addition to a vacuum vapor deposition. When the organic EL element is used as the light-emitting element in the above-mentioned exposure device, the productivity of the exposure device improves. Further, time-consuming tasks can be eliminated for adjusting the layout positions of the respective light-emitting elements. Thus, the layout positions are maintained with high precision. With respect to the substrate on which a light-emitting array is formed, a TFT (thin-film transistors) substrate is often used. Moreover, each light-emitting element is allowed to perform an exposure gradation control in multiple stages by modulating at least one of the light-emitting intensity and exposing time so as to control the exposure gradations.
Here, the exposure device of the invention is applicable to an exposure device of silver halide color photosensitive material. By using the silver halide color photosensitive material that is superior in gradation expressing property and gradation reproducibility, the exposure device of the present invention can achieve faithful reproducing a great number of exposure gradations.
In order to achieve still another object, according to a third aspect of the invention, there is provided an exposure device which exposes a photosensitive material comprising a light-emitting element array and a control device as follows. The light-emitting element array has matrix electrodes that include a plurality of cathodes and a plurality of anodes arranged in a lattice shape. The matrix electrodes are divided into a plurality of areas in the cathode aligning direction or the anode aligning direction and light-emitting elements that are provided at intersections of the matrix electrodes. The driving device applies a voltage between the cathode and anode with respect to each of the divided areas, and independently drives the light-emitting elements that are provided at intersections of the matrix electrodes in the corresponding area so as to be lighted on.
There is a case where the light-emitting array is constituted by matrix electrodes in which a plurality of anodes and a plurality of cathodes are arranged in a lattice shape with light-emitting elements being placed at the intersections of these matrix electrodes. In this case, the matrix electrodes of the light-emitting array are divided into a plurality of areas in the cathode array direction or the anode array direction. The driving device carries out a driving process independently to apply a voltage between the above-mentioned cathode and anode in order to light the light-emitting element placed at the intersection of the matrix electrodes of the corresponding area.
In comparison with a case in which the entire light-emitting element group is driven, the number of light-emitting elements to be assigned to each cathode or each anode reduces. Thereby the driving duty of each light-emitting element improves and the peak light-emitting intensity decreases. This is due to dividing the matrix electrodes into a plurality of areas and applying a voltage between the above-mentioned cathode and anode for each of the areas. These driving and applying a voltage are for driving independently to activate the light-emitting element placed on each intersection of the matrix electrodes in the area (for example, passive-matrix driving). Consequently, the reliability of the exposure device improves.
Here, the driving duty refers to a ratio t/T of the pulse width t with respect to the pulse repeating frequency T when the light-emitting elements are pulse-driven. Because the exposing efficiency improves by improving the driving duty, the peak light-emitting intensity of each light-emitting element reduces.
When the exposure device is provided with a plurality of kinds of light-emitting elements having different light-emitting spectra, the area in which light-emitting elements having the lowest sensitivity to the photosensitive material (that is, emitting light having such light-emitting spectra) may be driven independently of other areas. In this case, the peak light-emitting intensity of the light-emitting elements having the lowest sensitivity lowers and the reliability of the exposure device improves.
In an exposure device having a plurality of kinds of light-emitting elements, the number of rows of light-emitting elements that emit light having the lowest sensitivity to the photosensitive material in the plurality of kinds of light-emitting elements is made greater than any number of rows of other kinds of light-emitting elements. Thus, the light-emitting intensity (time average) reduces of the light-emitting elements having the lowest sensitivity to the photosensitive material. Thereby the reliability of the exposure device improves.
Moreover, the light-emitting elements of a plurality of kinds may be prepared as three kinds of light-emitting elements having light-emitting spectra that are capable of forming a full color image in association with the photosensitive materials. For example, the three kinds of light-emitting elements may be prepared as red light-emitting elements for emitting red light, green light-emitting elements for emitting green light and blue light-emitting elements for emitting blue light. Thus, a full-color image (latent image) can be formed.
In the above-mentioned exposure device, organic EL elements, which are easily formed into an array, are often used as light-emitting elements. A number of organic EL elements can be formed on a single substrate by using a coating method and an ink-jet method in addition to a vacuum vapor deposition. When the organic EL element is used as the light-emitting element in the above-mentioned exposure device, the productivity of the exposure device improves, and time-consuming tasks for adjusting the layout positions of the respective light-emitting elements can be eliminated. Thus, the layout positions are maintained with high precision. Moreover, each light-emitting element is allowed to perform an exposure gradation control in multiple stages, that is, mi (i=1 to p) stages by modulating at least one of the light-emitting intensity and exposing time so as to control the exposure gradations.
Here, the exposure device of the present invention may often be used as an exposure device for a silver halide color photosensitive material. By using the silver halide color photosensitive material, the exposure device of the present invention can faithfully reproduce an increased number of exposure gradations.
When a silver halide photosensitive material is used as the photosensitive material, a full-color image by using three kinds of light-emitting elements of red, green and blue can be formed. Red light-emitting elements having the lowest sensitivity to the photosensitive material may be formed at intersections in a predetermined divided area of the matrix electrodes in the light-emitting element array while green and blue light-emitting elements are formed at intersections in other divided areas.